Connecting elements for producing hybrid electronic circuits

BACKGROUND OF THE INVENTION

00011. Field of the Invention

0002The invention relates to the interconnection of electronic components, and especially applies in flip-chip type hybridizations.

00032. Description of Related Art

0004“Flip-chip” hybridization or “face-to-face” hybridization generally comprises forming two electronic circuits independently from each other, and placing them one on top of the other by means of interconnects both ensuring the positive mechanical connection function and the electric connection function. For example, an imager comprises, on the one hand, an array detection circuit comprising an array of photosites sensitive to electromagnetic radiation and, on the other hand, a circuit comprising electronics for reading the array of photosites. The two circuits are usually manufactured independently from each other, and then hybridized.

0005The first flip-chip hybridization comprised hybridizing circuits by means of solder balls, usually made of indium which, once solid, would positively connect the circuits together while forming electric connections. This type of hybridization however does not allow a high density of connections per surface area unit, and thus imposes a limit to the miniaturization of electronic components. Further, a step of heating under a reducing atmosphere is necessary during the hybridization to melt the solder balls, thereby preventing the use of materials or electronic components which cannot withstand such a heating.

0006Finally, the hybridization by means of a soldering is definitive since it requires creating intermetallic compounds between the solder material and the material having the soldering performed thereon. The material having the soldering performed thereon is thus modified and cannot be used twice. Part of the solder is further consumed, making a separation and resoldering impossible without losing quality. The definitive character of the soldering is strongly limiting in terms of quality control and of defective circuit repair. Thus, for example, to test the operation of the imager detection circuit, it is necessary to couple it with a read circuit. Since this coupling is performed by soldering, the read circuit in charge of the test is thus necessarily the final read circuit. As a result, if the detection circuit appears to be defective, the read circuit is also rejected since it is permanently coupled thereto, even though it would be perfectly operable. Similarly, in case of a failure of one or the other of the circuits, replacing the defective circuit is impossible. The hybrid assembly is then rejected, thus including the circuit still in perfect operating condition.

0007More recently, an alternative to solder balls, schematically illustrated in <figref idref="DRAWINGS">FIG. 1</figref> and described in document FR 2936359, provides the forming of male and female cylindrical inserts <b>10</b> and <b>12</b> on surfaces of a first and of a second circuit <b>14</b>, <b>16</b>, and the placing of first circuit <b>14</b> on second circuit <b>16</b> by insertion of male insert <b>10</b> into female insert <b>14</b>.

0008Although the manufacturing of such inserts is possible with a high surface area density due to the techniques used, this solution is in practice poorly viable. Indeed, male insert <b>10</b> and female insert <b>12</b> should form together a reliable electric connection, which thus means that the external diameter of male insert <b>10</b> is substantially equal to the intern al diameter of female insert <b>12</b> for their surfaces to be in contact. The insert manufacturing process should thus be extremely precise, just as the process of insert alignment for the insertion of the male insert into the female insert.

0009Document JP 01226160 provides a similar interconnection, the main difference being that the male insert is solid and has an external diameter selected to obtain a force-fitting into the female insert with a resilient and plastic deformation thereof. Here again, this requires a very high precision in manufacturing and alignment processes. Further, due to the materials used, that is, metals to obtain an electric connection, the deformation of the female insert is non-reversible. Indeed, the male and female inserts are interconnected by force-fitting by using a plastic deformation of the materials, and thus an irreversible deformation thereof. Once hybridized, it is thus no longer possible to separate the two circuits without causing the destruction of the female elements.

0010To overcome these problems, it is possible to fill the female insert with a solder material <b>20</b>, as illustrated in <figref idref="DRAWINGS">FIG. 2</figref> and described in document FR 2936359. Thereby, solder material <b>20</b> forms an electric joint between male insert <b>12</b> and female insert <b>14</b>, thus enabling to slacken the constraints relative to their manufacturing or alignment precision.

0011The reintroduction of a solder material in the circuit interconnection however brings about disadvantages inherent to this type of hybridization, that is, the need for a heating, as well as the definitive aspect of the hybridization, as previously explained.

SUMMARY OF THE INVENTION

0012The present invention aims at providing an interconnect which does not require using a high-precision manufacturing and alignment process, which does not require the use of solder material, and which is reversible. It also aims at doing away with the issue relative to the guiding of the connection elements with respect to each other.

0013For this purpose, the invention aims at a female connection element comprising a hollow flared portion for receiving and guiding a male connection element and a hollow mating portion, formed in extension of the flared portion, for mating with the male connection element, wherein the mating portion is made of a deformable material and has a corrugated transverse cross-section having an internal diameter before the mating smaller than the external diameter of the male element before the mating, to expand when the part to be mated of the male connection element is fitted into it.

0014In other words, the flared shape of the female element enables to receive a male element without requiring an accurate alignment and to guide it towards the portion of the female element with which it is intended to cooperate to form the electric and mechanical connection. Further, this flared shape having a “generally” decreasing diameter, the walls of the male element and of the female element necessarily come into contact with each other, and this, even if the manufacturing process used for their construction is imprecise.

0015Further, due to the corrugated shape of the mating portion of the female element, the force-fitting of the male element does not cause a significant stretching of the material forming this portion. Thus, the deformation undergone is not irreversible and the removal of the male element causes the returning of the mating portion to a shape close to the initial shape. The male element can thus be inserted back into the female element while providing an electric and mechanical connection of identical quality.

0016The interconnection is thus not definitive. Two circuits hybridized by means of such connection elements may thus be separated, for example, for testing, replacement, or other reasons, and be hybridized again.

0017The invention also aims at a male connection element intended to cooperate with a female connection element which comprises a hollow flared portion for receiving and guiding the male connection element and a hollow mating portion, formed in extension of the flared portion, for mating with the male connection element, wherein a portion to be mated of the male connection element is made of a deformable material and has a corrugated transverse cross section having an external diameter before the mating greater than the internal diameter before the mating of the mating portion of the female element, to contract when it is fitted into the mating portion.

0018In other words, the portion to be mated of corrugated cross-section ensures the reversibility of the interconnection, for reasons similar to those described hereabove.

0019The invention also aims at a system for connecting a first component to a second component, comprising at least a pair of male and female connection elements respectively attached to the first and second components. According to the invention: <ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0000"><ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0020">a female connection element comprises a hollow flared portion for receiving and guiding the male connection element and a hollow mating portion, formed in extension of the flared portion, for mating with the male connection element;</li><li id="ul0002-0002" num="0021">a portion to be mated of the male connection element has an external diameter before the mating greater than an internal diameter of the mating portion of the female connection element;</li><li id="ul0002-0003" num="0022">and the portion to be mated of the male connection element is made of a deformable material and has a corrugated transverse cross-section, to contract when it is fitted into the mating part of the female element, and/or the mating part of the female connecting element is made of a deformable material and has a corrugated transverse cross-section, to expand when the portion to be mated of the male element is fitted into it.</li></ul></li></ul>

0023The invention also aims at a method for manufacturing a female connection element of the above-mentioned type, comprising: <ul id="ul0003" list-style="none"><li id="ul0003-0001" num="0000"><ul id="ul0004" list-style="none"><li id="ul0004-0001" num="0024">forming a layer capable of being etched;</li><li id="ul0004-0002" num="0025">depositing on the layer capable of being etched a layer insensitive to etching comprising an opening having a corrugated profile;</li><li id="ul0004-0003" num="0026">applying an isotropic etching on the opening to form, in the layer capable of being etched, the flared portion;</li><li id="ul0004-0004" num="0027">applying an anisotropic etching on the opening to form, in the layer capable of being etched, the mating portion; and</li><li id="ul0004-0005" num="0028">removing the layer insensitive to etching</li></ul></li></ul>

0029The invention also aims at a method for manufacturing a female connection element of the above-mentioned type, comprising: <ul id="ul0005" list-style="none"><li id="ul0005-0001" num="0000"><ul id="ul0006" list-style="none"><li id="ul0006-0001" num="0030">forming a stack of at least one upper layer and one lower layer capable of being etched, the upper layer being etched more rapidly than the lower layer;</li><li id="ul0006-0002" num="0031">depositing on the upper layer a layer insensitive to etching and comprising an opening having a corrugated profile;</li><li id="ul0006-0003" num="0032">applying an etching to the opening to form, in the at least two layers capable of being etched, the flared portion and the mating portion;</li><li id="ul0006-0004" num="0033">removing the layer insensitive to etching</li></ul></li></ul>

0034According to an embodiment, the layer(s) capable of being etched are polymer layers of diimide type.

0035According to an embodiment of the invention, the method comprises depositing a metal layer on the internal wall of the etched portions.

0036According to an embodiment of the invention, the method comprises removing the layer(s) capable of being etched.

BRIEF DESCRIPTION OF THE DRAWINGS

0037The present invention will be better understood on reading of the following description provided as an example only in relation with the accompanying drawings, where the same reference numerals designate the same or similar elements, among which:

0038<figref idref="DRAWINGS">FIG. 1</figref> is a simplified cross-section view of an interconnect according to a first state of the art;

0039<figref idref="DRAWINGS">FIG. 2</figref> is a simplified cross-section view of an interconnect according to a second state of the art;

0040<figref idref="DRAWINGS">FIG. 3</figref> is a simplified cross-section view of an interconnect according to the invention;

0041<figref idref="DRAWINGS">FIG. 4</figref> is a simplified cross-section view along plane A-A of <figref idref="DRAWINGS">FIG. 3</figref>;

0042<figref idref="DRAWINGS">FIG. 5</figref> is a simplified cross-section view along plane B-B of <figref idref="DRAWINGS">FIG. 3</figref>;

0043<figref idref="DRAWINGS">FIGS. 6 and 7</figref> are simplified cross-section views illustrating the reception and the guiding of the male element by the flared portion of the female element;

0044<figref idref="DRAWINGS">FIG. 8</figref> is a diagram illustrating the mating portion of the female connection element before the mating and after the mating with the male element;

0045<figref idref="DRAWINGS">FIGS. 9 to 17</figref> are simplified cross-section views illustrating a first method for manufacturing a female connection element according to the invention;

0046<figref idref="DRAWINGS">FIGS. 18 and 19</figref> are simplified cross-section views illustrating an interconnect with a filling material between the two hybridized circuits; and

0047<figref idref="DRAWINGS">FIGS. 20 and 21</figref> are simplified cross-section views illustrating a second method for manufacturing a female connection element according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

0048<figref idref="DRAWINGS">FIG. 3</figref> shows an interconnect according to the invention. It comprises a hollow female metal connection element <b>30</b> comprising a flared portion <b>32</b> continued by a mating portion <b>34</b>.

0049As shown in <figref idref="DRAWINGS">FIGS. 4 and 5</figref>, which are respective cross-section views along planes A-A and B-B of <figref idref="DRAWINGS">FIG. 3</figref>, female element <b>30</b> has a corrugated transverse cross-section, with an inscribed circle <b>36</b> of opening <b>38</b> having its diameter decreasing in flared portion <b>32</b> from opening <b>38</b> of female element <b>30</b> to mating portion <b>34</b>, and having a substantially constant inscribed diameter <b>36</b> in mating portion <b>34</b>.

0050Male connection element <b>10</b> takes the shape of a hollow metal cylinder. Its external diameter is smaller than the diameter of the inscribed circle <b>36</b> of opening <b>38</b> of female element <b>30</b>, but is greater than inscribed diameter <b>36</b> of mating portion <b>34</b> of female element <b>30</b>.

0051The materials forming male and female connection elements <b>10</b> and <b>30</b> are advantageously selected from among Cu and its compounds (CuBe, for example), Ni and its compounds (NiBe, for example), W and its compounds (WN and WSi, for example), Ti and its compounds (TiN and TiW, for example), Au and its compounds (AuSn, for example), and Pt and its compounds (PtSi, for example).

0052More specifically, the materials are selected to be both robust and fine electric conductors. Advantageously, the male elements may be made of a first material having a good mechanical resistance, such as, for example, CuBe, covered with a second material having a fine electric conduction, such as Au, for example.

0053As illustrated in <figref idref="DRAWINGS">FIGS. 6 and 7</figref>, flared portion <b>32</b> of female element <b>30</b> has the function of receiving male element <b>10</b> and of guiding it towards mating portion <b>34</b>.

0054Advantageously, the inscribed diameter of opening <b>38</b> of female element <b>30</b> is larger than the external diameter of male element <b>10</b> by at least accuracy dL of the tool used to position male element <b>10</b> above female element <b>30</b> during the hybridizing of electronic circuits <b>14</b>, <b>16</b>. Thereby, it is ensured that male element <b>10</b> is inserted into female element <b>30</b>.

0055Flared shape <b>32</b> further allows a self-alignment of elements <b>10</b> and <b>30</b>. Indeed, when male element <b>10</b> comes into contact with the internal wall of flared portion <b>32</b>, the vertical force exerted on this inclined wall creates in reaction a horizontal component which automatically aligns the two connection elements <b>10</b> and <b>30</b>, as can be seen in <figref idref="DRAWINGS">FIG. 7</figref>. Male element <b>10</b> is thus perfectly aligned with the opening of mating portion <b>34</b>.

0056The actual fitting of male element <b>10</b> into female element <b>30</b> is then performed by vertically pushing the male element into mating portion <b>34</b>. Portion <b>34</b>, which has an inscribed diameter <b>36</b> smaller than the external diameter of male element <b>10</b>, then easily expands due to its corrugated profile, combined with the fact that it is formed of a deformable material, here a metal.

0057<figref idref="DRAWINGS">FIG. 8</figref> illustrates the transverse cross-section of mating portion <b>34</b> before and after the mating of male element <b>10</b>. As can be seen in this drawing, the cross-section of portion <b>34</b> passes from a corrugated profile <b>34</b><i>a </i>to a convex profile <b>34</b><i>b </i>having male element <b>10</b> inscribed therein. The element, force-fitted into mating portion <b>34</b>, is then in contact therewith at many points, thus providing a reliable electric connection between the two connection elements <b>10</b>, <b>30</b>.

0058“Deformable” here means a material capable of undergoing the deformation caused by the force-fitting of the male element into mating portion <b>34</b> with no damage and reversibly. In practice, the deformability thus depends not only on the very nature of the material, but also on the thickness of the walls of mating portion <b>34</b> and on it corrugated profile. Still in practice, it is possible for any material to acquire this deformation quality, provided for the thickness and/or the corrugated profile to be appropriately selected.

0059Vertical force “F” exerted on male element <b>10</b> for its fitting into mating portion <b>34</b> of female element <b>30</b> determines the mating depth according to the involved geometries. As soon as the vertical resultant of the deformation forces is equal to force “F” exerted on the male element, the insertion is stopped.

0060Assuming as a first approximation that the deformation undergone by mating portion <b>34</b> is resilient, the de-inserting of the male element then requires a force opposite to force “F”, mating portion <b>34</b> substantially returning to its initial shape as element <b>10</b> is being removed. It should thus be noted that the corrugated transverse profile of portion <b>34</b> behaves as a spring. Thus, it is possible to mate and unmate male and female elements <b>10</b> and <b>30</b> as often as desired.

0061In the described embodiment, male element <b>10</b> is a hollow metal cylinder. It is thus also deformed during its fitting. As a variation, the male element may be solid, in which case it undergoes substantially no deformation.

0062Further, the shape of the male element is not limited to a cylinder. The male element may for example be wider at its bottom than at its top, which enables to enhance the mechanical hold.

0063Further, an embodiment where the female element has a corrugated profile in its mating portion to be able to undergo a reversible deformation due to a spring effect has been described. As a variation, or complementarily to the corrugated profile of female element <b>30</b>, the male element has a corrugated transverse cross-section so that it undergoes during its fitting a reversible contraction also implementing a spring effect.

0064Advantageously, both the male element and the female element have such a corrugated profile, so that the force necessary to plug these two elements is decreased.

0065It should further be noted that it is also possible to provide a filling of the female element with a solder material which fills the space between the male element and the female element and thus form an electric and mechanical joint. The use of a solder material obviously depends on the targeted application, but it should be noted that the corrugated profile of the male element and/or of the female element remains very advantageous. Indeed, for example, before definitively hybridizing two circuits together by using a solder material, preliminary tests may be carried out on each of them. A hybridization with no welding material is thus advantageously implemented, exploiting the reversibility of the mating of the male and female elements. Once tested and approved, the circuits are then ready for a definitive hybridization with the solder material.

0066Similarly, independently from the provided possibility of performing tests with a reversible mating, it should be noted that the force exerted to obtain a reliable mating of the female and male elements is much lower in the invention than the force necessary to force-fit male and female elements of circular cross-section. It should be noted on this regard that the stronger the exerted force, the more crucial the control of its verticality. Indeed, the transverse component of a non-vertical force induces a non-negligible risk of breakage of one or the other of the connection elements. It should easily be understood how delicate it can be to force-fit elements having walls of a thickness smaller than one micrometer.

0067A method for manufacturing female elements with a corrugated transverse cross-section on the surface of a microelectronic circuit to be hybridized will now be described in relation with <figref idref="DRAWINGS">FIGS. 9 to 17</figref>.

0068The male connection elements are hollow metal cylinders for example formed by means of the method described in document FR 2928033.

0069The method starts (<figref idref="DRAWINGS">FIG. 9</figref>) with the deposition, on surface <b>50</b> to be hybridized of a microelectronic circuit <b>16</b>, of a so-called “sacrificial” layer <b>54</b> sensitive to etching, and preferentially formed in a polymer of polyimide type. This polymer has the advantage of withstanding high process temperatures, on the order of 350-400° C., for example, used during the deposition.

0070A layer <b>56</b> made of a hard material insensitive to etching, for example, made of SiO, of SiN, or of metal, is then deposited on sacrificial layer <b>54</b>, after which openings <b>58</b> are formed through hard layer <b>56</b> at the locations desired for the female connection elements (<figref idref="DRAWINGS">FIG. 9</figref>).

0071Openings <b>58</b>, illustrated in top view in <figref idref="DRAWINGS">FIG. 10</figref>, are for example formed by photolithography by means of a mask, as known per se in the state of the art. Openings <b>58</b>, all identical in the example, have a corrugated profile, are inscribed in an external circle “Cext” <b>60</b>, and have an internal inscribed circle “Cint” <b>62</b>.

0072As a numerical example, sacrificial layer <b>54</b> has a <b>5</b>-micrometer thickness, diameter Cext of openings <b>58</b> is equal to 5.5 micrometers, and diameter Cint of openings <b>58</b> is equal to 4.5 micrometers.

0073The method then continues (<figref idref="DRAWINGS">FIG. 11</figref>) with the application of a partial isotropic etching of sacrificial layer <b>54</b> through openings <b>58</b>, that is, an isotropic etching which is not performed across the entire thickness of layer <b>54</b>. The etching is for example performed by application of a high-pressure O₂plasma without the assistance of a directional ion bombarding or by application of a liquid chemical product, such as a liquid polyimide etching described in document U.S. Pat. No. 4,846,929 or an etching with TMAH (tetramethylammonium hydroxide).

0074The isotropic etching thus etches the polymer of sacrificial layer <b>54</b> in all directions. As can be seen in <figref idref="DRAWINGS">FIG. 12</figref>, a lateral overetching <b>60</b> is performed under hard layer <b>56</b>. Further, the isotropic etching etches sacrificial layer <b>54</b> according to an isotropy slope <b>62</b>, having its value depending on the features of the etching process. For example, in an oxygen plasma etching, by varying the voltage between the electrodes for controlling plasma discharges, a vertical anisotropic mechanical “ion” assistance is created. More specifically, isotropy slope <b>62</b> increases if the voltage increases. It should be noted that other parameters may be varied and that the control of the isotropy slope is a perfectly-controlled mechanism.

0075Especially, as concerns the obtaining of isotropy slope <b>62</b>, several tests with different parameter values may be carried out until the desired isotropy slope <b>62</b> is obtained.

0076Different parameters of the plasma etch method may be varied, in particular: <ul id="ul0007" list-style="none"><li id="ul0007-0001" num="0000"><ul id="ul0008" list-style="none"><li id="ul0008-0001" num="0077">the etching time,</li><li id="ul0008-0002" num="0078">the gas flow rate (essentially oxygen, nitrogen),</li><li id="ul0008-0003" num="0079">the gas pressure: for example, when the pressure increases in the etch chamber, the etching is more isotropic.</li><li id="ul0008-0004" num="0080">the power: <ul id="ul0009" list-style="none"><li id="ul0009-0001" num="0081">applied to the wafer: by increasing this power, the etching is more anisotropic</li><li id="ul0009-0002" num="0082">applied to the source: by increasing this power, the etching is more isotropic,</li></ul></li></ul></li></ul>

0083Flared portion <b>32</b> of the female connection elements is thus formed.

0084Further, the etching, be it isotropic or not, etches sacrificial layer <b>54</b> so that, whatever the considered height in sacrificial layer <b>54</b>, the transverse cross-section of an etched portion of sacrificial layer <b>54</b> is homothetic to the corresponding opening <b>58</b>.

0085In the numerical example, the isotropy slope is equal to 30° during the etching of the first two micrometers of sacrificial layer <b>54</b>, that is, each micrometer of etching through the thickness of sacrificial layer <b>54</b> results in a lateral widening of the dimensions by 0.5 micrometer per side under hard layer <b>56</b> and in no widening at the bottom of the etching Thus, by stopping the etching when it has etched 2 micrometers of the thickness of sacrificial layer <b>54</b>, the portion etched in an opening <b>58</b> is characterized, sizewise, by: <ul id="ul0010" list-style="none"><li id="ul0010-0001" num="0000"><ul id="ul0011" list-style="none"><li id="ul0011-0001" num="0086">under hard layer <b>56</b>: <ul id="ul0012" list-style="none"><li id="ul0012-0001" num="0087">an inner circle having its diameter increasing from 4.5 to 6.5 micrometers;</li><li id="ul0012-0002" num="0088">an outer circle having its diameter increasing from 5.5 to 7.5 micrometers;</li></ul></li><li id="ul0011-0002" num="0089">at a depth of 2 micrometers under hard mask <b>56</b>: <ul id="ul0013" list-style="none"><li id="ul0013-0001" num="0090">an inner circle having its diameter remaining at 4.5 micrometers;</li><li id="ul0013-0002" num="0091">an outer circle having its diameter remaining at 5.5 micrometers.</li></ul></li></ul></li></ul>

0092In practice, the dimensions of openings <b>58</b> are selected to take into account lateral underetching. Thus, for example, if the male element intended to cooperate with a female element is a cylinder having a diameter equal to 5 micrometers, and the precision of the machines used to mate the male and female elements is equal to 0.5 micrometer, openings <b>58</b> in the hard mask are selected so that their outer circle has a diameter equal to 5.5 micrometers and their inner circle has a diameter equal to 4.5 micrometer, thus providing flared upper portions of the female elements having an internal circle diameter at the opening equal to 6.5 micrometers compatible with the precision of the machines.

0093The method then carries on with the application of an anisotropic etching across the remaining thickness of sacrificial polymer layer <b>54</b>, such as for example the application of a low-pressure O₂plasma assisted by a directional ion bombarding (<figref idref="DRAWINGS">FIGS. 13 and 14</figref>) or for example the application of an ion etching.

0094The anisotropy of the etching thus results in applying the geometry of openings <b>58</b> to the remaining thickness of sacrificial layer <b>54</b> with no lateral overetching. Mating portion <b>34</b> of the female connection elements is thus formed in extension of flared portion <b>32</b> with a transverse cross-section substantially identical to the profile of openings <b>58</b>, and thus especially a corrugated transverse cross-section having a diameter of its inscribed circle equal to 4.5 micrometers in the numerical example.

0095The method then carries on with the conformal deposition of a hard metal layer <b>64</b>, advantageously made of CuBe, over the surface of the assembly (<figref idref="DRAWINGS">FIG. 15</figref>), that is, the thickness of the hard metal deposition is constant over the entire surface that it covers, including on flared portion <b>32</b>. Advantageously, a CVD (chemical vapor deposition) is performed to form hard metal layer <b>64</b>.

0096Hard metal layer <b>64</b> thus deposits on the internal wall of the etched portions of sacrificial layer <b>54</b>, which enables to form mechanically resistant and electrically conductive walls. Preferably, the deposition is performed by means of a chemical vapor deposition, this type of deposition ensuring a good conformality of the layer deposited on the wall of the etched portions. For example, a copper layer having a 0.2-micrometer thickness is deposited.

0097A mechanical polishing is then carried out to remove hard metal layer <b>64</b> and hard layer <b>56</b> from the surface of the assembly, to expose sacrificial layer <b>54</b> (<figref idref="DRAWINGS">FIG. 16</figref>) and electrically isolate the female connection elements from one another.

0098In a first variation, the method carries on with the removal of sacrificial layer <b>54</b>, to disengage female connection elements <b>30</b> (<figref idref="DRAWINGS">FIG. 17</figref>). The method then optionally carries on with the deposition on female elements <b>30</b> of a gold layer, for example, having a 0.1-micrometer thickness, to preserve a good surface quality. Such a gold layer especially enables to avoid an oxidation of the hard material of female elements <b>30</b> when the component is stored before use. Indeed, when no specific precaution is taken, a native oxide naturally forms at the surface of the hard material of female elements <b>30</b>, which adversely affects the quality of the electric connection subsequently formed with the male elements.

0099Similarly, the male connection elements are also covered with a gold layer. This is for example performed by depositing a gold layer, and then etching by means of a mask enabling to etch the gold layer around each male and female connection element, to only cover them with a gold layer, with an optional overlapping of a limited area around each of them.

0100In a second alternative embodiment, sacrificial layer <b>54</b> is maintained to form a filling material between the two hybridized circuits, as shown in <figref idref="DRAWINGS">FIGS. 18 and 19</figref>, which show the circuits to be hybridized respectively before and after the mating of male and female elements <b>10</b> and <b>30</b>. It should be noted that the material of sacrificial layer <b>54</b>, preferentially a polymer of diimide type, has a resilience enabling it to deform on insertion of the male elements, which enables to keep the sacrificial layer and thus to increase the mechanical resistance of the assembly once the circuits have been hybridized.

0101Thus, method steps are spared since the hybridization by means of hollow elements is usually completed with a coating step to protect the elements, which are more fragile than solder ball interconnects used in prior art. Further, sacrificial layer <b>54</b> has by construction a good flatness due to the process used to remove hard layers <b>56</b> and <b>64</b>, which enables to correct the lack of flatness of the lower substrate, to improve connection efficiencies. Further, due to polyimide of sacrificial layer <b>54</b>, possible height differences, such as steps, for example, can be compensated.

0102Advantageously, should the application require it, surface <b>66</b> of second circuit <b>14</b> having male elements <b>10</b> formed thereon is covered with a layer <b>68</b> of polymerizable material, and advantageously a material polymerizable in two steps, such as for example an epoxy resin, such as disclosed in document U.S. Pat. No. 7,579,392. This type of resin, commonly called “Bstage”, has the advantage of reticulating in two heating steps. In a first heating step at a first temperature, the resin partially reticulates and passes from a liquid state to a malleable state, which enables to shape it. After a second heating step, at a second temperature higher than the first temperature, the resin then completely reticulates and thus becomes solid.

0103This enables to bond first and second circuits <b>14</b> and <b>16</b> together after hybridization by “face-to-face” bonding, with layer <b>68</b> of polymerizable material being spread in a thin film when in its malleable state after the first heating step, and then positive connecting circuits <b>14</b> and <b>16</b> by the solidification of layer <b>68</b> of polymerizable material after the second heating step, as for example described in document U.S. Pat. No. 7,579,392.

0104Optionally and according to the targeted application, the internal surface of female elements <b>30</b> is covered with a layer of solder material <b>70</b> to form a mechanical and electric joint once the male elements have been fitted.

0105As mentioned hereabove, the male connection elements are for example formed by means of the method described in document FR 2928033.

0106As a variation, the male elements may be formed similarly to the previously-described method by etching a sacrificial layer by means of a purely anisotropic etching. The openings formed in the hard layer covering the sacrificial layer are circular, in which case cylindrical and hollow male elements are obtained, or have a corrugated profile, in which case hollow male elements of corrugated transverse cross-section are obtained.

0107In the previously-described method, the height of flared portion <b>32</b> of the female connection elements is determined by the duration of the isotropic etching applied to sacrificial layer <b>54</b>. Now, however neatly the material of sacrificial layer <b>54</b> is formed and the etching is performed, inhomogeneities may nevertheless appear during the etching, thus resulting in flared portions <b>32</b> of different heights, and thus in a subsequent hybridization of poorer quality.

0108A second method for manufacturing the female connection elements according to the invention, enabling to more precisely control the height of the flared portions of the female connection elements, and this whatever the quality of the etched material and whatever the quality of the etching, will now be described in relation with <figref idref="DRAWINGS">FIGS. 20 and 21</figref>.

0109According to this second embodiment, sacrificial layer <b>54</b> is replaced with a stack of two polymer layers <b>70</b>, <b>72</b>, advantageously of diimide type, which are etched at different rates (<figref idref="DRAWINGS">FIG. 20</figref>), upper polymer layer <b>70</b> being etched faster than lower polymer layer <b>72</b>.

0110An isotropic etching is then performed in upper polymer layer <b>70</b> all the way to lower polymer layer <b>72</b>, similarly to the isotropic etching of sacrificial layer <b>54</b> of the previous embodiment. Flared portions <b>32</b> are then formed. Especially, just as for the previous embodiment, the profile of openings <b>58</b> is transferred to the etched portions which thus have sections homothetic to the profile.

0111However, unlike in the previous embodiment, lower polymer layer <b>72</b> here is used as a stop layer for the etching performed in upper polymer layer <b>70</b>. Especially, by selecting a lower polymer layer <b>72</b> etched at a much lower rate than upper polymer layer <b>70</b>, the etching thereof substantially stops at the interface with lower polymer layer <b>72</b>. The height of flared portions <b>32</b> is then set by the height of upper polymer layer <b>70</b>, and thus by its forming process, that is, for example, the deposition process used.

0112The method then carries on with the application of an anisotropic etching, which then forms in lower polymer layer <b>70</b> mating portions <b>34</b> of the female connection elements, similarly to the first embodiment (<figref idref="DRAWINGS">FIG. 21</figref>). Especially, as for the previous embodiment, the profile of openings <b>58</b> is transferred to the etched portions, which then have sections homothetic to the profile.

0113Advantageously, upper and lower polymer layers <b>70</b> and <b>72</b> are etched during a same etch process, for example, by means of an O₂plasma etching. As known per se, the isotropic and anisotropic character of the etching may be set by means of the voltage used for the plasma discharge.

0114Once the upper and lower sacrificial layers have been etched, the method then carries on similarly to the method according to the first embodiment.

0115The present invention provides the following advantages: <ul id="ul0014" list-style="none"><li id="ul0014-0001" num="0000"><ul id="ul0015" list-style="none"><li id="ul0015-0001" num="0116">a simplified positioning of the male element in front of the female element, which requires no high-precision tools. This positioning may further be performed at ambient temperature while the state of the art using solderings requires taking the assembly to at least the melting temperature of the solder material, and/or taking the assembly to a very high pressure to decrease the melting temperature of the solder material;</li><li id="ul0015-0002" num="0117">an intrinsic self-alignment of the male and female elements;</li><li id="ul0015-0003" num="0118">a reversible mating, since the male and female elements may be mated and unmated if necessary. This enables to replace defective circuits, to previously test the circuits to be hybridized, advantageously by means of a limited number of test circuits, or a single one, specifically designed for this purpose;</li><li id="ul0015-0004" num="0119">the possibility not to use a solder material to provide an electric connection. The absence of solder material especially enables to take the hybridized assembly to high temperatures if necessary, as for example in the case of a board soldering. Indeed, in the absence of solder material, no specific precaution is to be taken relative to the interconnections between male and female elements;</li><li id="ul0015-0005" num="0120">a low fitting force sufficient to mate the male and female elements;</li><li id="ul0015-0006" num="0121">a less expensive mating method, capable of operating at a high rate. Indeed, a positioning machine of “pick and place” type, which is fast but may have a limited precision, may be used to pre-insert the male elements into the female elements at a high rate, that is, partially mating these elements due to the intrinsic self-alignment according to the invention, after which the circuits thus partially hybridized may be displaced together with no risk of misalignment to another specific machine which performs the final mating of all connection elements. A significant gain in production rate is thus obtained;</li><li id="ul0015-0007" num="0122">the possibility of creating “upgradeable” boards or multiple chip modules (MCM): a chip version may be replaced with a more advanced version due to the interconnects according to the invention. This type of hardware upgrading is both easy to implement by constructors and difficult to implement by other people which do not have tools allowing an alignment with a precision on the order of one micrometer.</li></ul></li></ul>